1. Field of the Invention
The present invention relates to automatic splitter shifting in a manually shifted compound transmission having a lever-shifted main section connected in series with an auxiliary splitter or splitter-and-range section. In particular, the present invention relates to a splitter control for transmissions of the type described for automatically implementing splitter up-shifts and/or splitter-and-range shifts during a manual lever shift when an engine governor event is encountered.
2. Description of the Related Art
Controller-assisted, manually shifted transmission systems are known in the prior art, as may be seen by reference to U.S. Pat. Nos. 5,582,558; 5,755,639; 5,766,111; 5,791,189; 5,974,906; 5,989,155 and 6,015,366, the disclosures of which are incorporated herein by reference.
Compound transmissions having a range and/or combined range- and splitter-type auxiliary transmission section are well known in the prior art, as may be seen by reference to U.S. Pat. Nos. 4,754,665 and 5,390,561, the disclosures of which are incorporated herein by reference.
Transmissions having manually shifted main sections and automatically shifted splitter sections are known in the prior art, as may be seen by reference to U.S. Pat. Nos. 5,435,212; 5,938,711; 6,007,455 and 6,044,721, the disclosures of which are incorporated herein by reference.
Compound transmissions having automatically implemented range shifting are well known in the prior art, as may be seen by reference to U.S. Pat. Nos. 5,911,787 and 5,974,906, the disclosures of which are incorporated herein by reference.
One technique for controlling engine fueling to thereby limit engine speed during manual gear shifting operations is commonly referred to as progressive shift governor control, as may be seen by reference to U.S. Pat No. 6,135,918, the disclosure of which is incorporated herein by reference. In progressive shift governor control, a linear engine speed limit, or governed engine speed limit, is typically established by specifying a first engine speed limit RPM1 at a first vehicle speed VS1, and a second engine speed limit RPM2 at a second vehicle speed VS2. The governed engine speed limit linearly increases from RPM1 to RPM2 between VS1 and VS2 and is held constant at RPM2 beyond VS2, wherein RPM2 is typically less than rated engine speed. Rated engine speed is defined for purposes of the present invention as the engine speed at which the engine produces an advertised horsepower value.
The purpose of progressive shift governor control is to gradually increase available engine speed (and thus more engine power) as vehicle speed increases between VS1 and VS2, wherein typical values for VS1 and VS2 are 0.0 and 40 mph, respectively. This engine speed limiting scheme accordingly encourages the vehicle operator to manually shift gears at lower engine speeds than may otherwise occur, particularly in the lower transmission gears, thereby resulting in fuel savings associated with more efficient engine operation.
While the progressive shift governor control feature achieves the goal of encouraging vehicle operators to shift at lower engine speeds, it has certain drawbacks associated therewith. For example, when descending a grade or when hauling a heavily loaded trailer on level ground, providing a hard limit on available engine speed can hinder the drivability of the vehicle. One example of such hindered drivability may occur when attempting an automatic up-shift during an engine progressive shift governor event when descending a downhill grade, or moving at speed on level ground in a heavily loaded condition under low throttle, hereinafter characterized as a coasting condition or coasting. When in the coasting condition, the engine is being forced by the inertia of the vehicle to rotate at a higher speed than is commanded by the engine controller. Under the control of the progressive shift governor control, the governed engine speed limit may cause the vehicle to enter into a coasting condition in which the vehicle is driving the engine at a speed greater than that permitted by the progressive shift governor control, irrespective of the throttle position, resulting in a negative driveline torque. If the operator attempts to select the next higher gear by depressing the splitter button under such a negative torque condition, it may not be possible to shift gears due to the negative torque. As a result, the operator may be forced to break torque by depressing the clutch so that the transmission may be shifted to splitter-neutral and then to splitter high for the desired up-shift, thereby overcoming much of the benefit of an automated shift.